Nepal’s Big One: Myth or Reality?

In Nepal, especially in Kathmandu, earthquakes and the potential destruction they can cause, are an important part of popular folklore: It’s not hard to come across someone who thinks a large earthquake is “due.” Nepal’s last major quake was in 1934 and a devastating earthquake is believed to take place once every 80 years. This means that the next “big one” – an earthquake of magnitude 8 or more – is almost due. But is there science to back this up?

Prakash Mathema/Agence France-Presse/Getty Images

Sunday evening’s earthquake, which had its epicenter in the Indian state of Sikkim, rocked neighboring Nepal, including Kathmandu.

Sunday evening’s 6.9-magnitude earthquake, which had its epicenter in the Indian state of Sikkim, rocked neighboring Nepal, including Kathmandu. As of midday Wednesday, the death toll had gone up to 91, of which six in Nepal. But this figure could rise further, with local media reporting 11 deaths in Nepal alone.

The earthquake was caused by movements within the same tectonic plates that, millions of years ago, were responsible for giving rise to the world’s tallest mountain range, the Himalayas. The Indian plate, which pushes upwards into the Eurasian plate, is responible for raising the Himalayas by one centimeter each year, according to a study by the U.S. Geological Survey. This also causes tremendous stress to build up within the Earth’s crust, which is relieved, periodically, through earthquakes. The Alpine-Himalayan belt, which extends from Java through the Himalayas out into the Atlantic region, is where 17% of the world’s major earthquakes take place.

So Nepalis, in fairness, have reason to worry. Their country sits on the Alpine-Himalayan belt where the Indian and Eurasian plates meet. This makes it the most seismically-active country in the region, John Bellini, a geo-physicist with U.S. Geological Survey, told India Real Time. “It’s an area that can have large earthquakes.”

Within Nepal, the Kathmandu valley is at greatest risk of all. Should an 8.1-magnitude earthquake like the one that hit the country in 1934 take place today, the damage would be far greater. At the time, around 4,000 people in the Kathmandu valley died and a fourth of all buildings collapsed. Today, more than two million people live in the valley and over 40,000 are likely to lose their lives should an earthquake of that magnitude repeat itself, according to estimates of Nepal’s National Society for Earthquake Technology. Over 60% of the buildings are likely to collapse and about half of the valley’s population would be made homeless, the group estimates.

There are several reasons why the damage would be so great in Kathmandu, specifically. The city itself sits on soft soil sediment, the basin of a prehistoric lake, and this amplifies the effects of the quake. On top of this, most of the buildings are poorly built and usually fail to adhere to basic safety standards, increasing their chances of collapsing during an earthquake. In addition, Kathmandu’s rapid urbanization has been mismanaged, resulting in many heavily-congested areas that make rescue operations difficult. The country’s emergency relief mechanisms also leave a lot of room for improvement.

What are the chances of an earthquake like the 1934 one happening again? “It always is a possibility,” said Mr. Bellini. “But it can also be another 100 years.”

Mr. Bellini said that since seismology is a young science, there is not sufficient data to give accurate estimates of what the historical frequency of earthquakes is. However, he estimated that “80 years wouldn’t be an unreasonable number for recurrent rate” for large earthquakes. That falls in line with popular beliefs in Nepal.

Some scientists also believe a “Great Central Himalayan Earthquake” in the region between Kathmandu and Dehradun, in India’s state of Uttarakhand, is long overdue. There hasn’t been a big earthquake there for several centuries, a significant interval that could lead to a major buildup of seismic stress and consequent earthquake.

In recent years, some small progress has been made. Earthquake experts have made efforts to teach people what to do in case of earthquakes and how to improve the safety of their buildings.

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